GB2274073A

GB2274073A - Metallic honeycomb body for catalytic convertors

Info

Publication number: GB2274073A
Application number: GB9326567A
Authority: GB
Inventors: Masayoshi Usui
Original assignee: Usui Kokusai Sangyo Kaisha Ltd
Current assignee: Usui Kokusai Sangyo Kaisha Ltd
Priority date: 1993-01-08
Filing date: 1993-12-30
Publication date: 1994-07-13
Anticipated expiration: 2013-12-30
Also published as: KR940018544A; US5372893A; JP3392895B2; KR100284531B1; JPH06205984A; GB2274073B; GB9326567D0; DE4400314A1

Abstract

Individual stacks (X1 to X2) have been formed by alternately stacking planar bands (1) and corrugated bands (2) one over the other into a predetermined number of layers and providing notched fitting portions (A1 to A2) at central parts of the individual stacks. The planar bands (1) are each made of a sheet metal, while the corrugated bands have been obtained by corrugating such planar bands. The notched fitting portions (A1 to A2) provided at the central parts of the individual stacks (X1 to X2) preferably have such a shape that, when the individual stacks are filled and combined together and are then rolled in the same direction about the notched fitting portions as a central axis of the rolling formation into an X-wrapped metallic honeycomb body (XH), the front face (XHF) and rear face of the metallic honeycomb body are planar. <IMAGE>

Description

2274073 X-WRAPPED METALLIC HONEYCOMB BODY BACKGROUND OF THE INVENTION

a) Field of the Invention

This invention relates to a metallic honeycomb body which is generally used in a form interposed as exhaust gas cleaning means in an exhaust pipe system of an automotive vehicle.

More specifically, this invention is concerned with an X-wrapped metallic honeycomb body for carrying, especially an exhaust gas cleaning catalyst thereon, said honeycomb body having an increased carrying sur face area in a central part thereof and improved durability.

b) Description of the Related Art

In automotive exhaust gas cleaning means of the above-described type, monolithic ceramic carrier bodies have been used to date. However, monolithic metallic carrier bodies are now attracting interests in place of such conventional carrier bodies.

In general, a metal-made, monolithic carrier body for carrying an exhaust gas cleaning catalyst is con structed from a honeycomb-shaped, multilayered com posite body (hereinafter called a %etallic honeycomb body") and a metallic cylindrical casing having opening at opposite ends thereof so that the metallic honeycomb body can be inserted into the casing and then fixed on the casing. The metallic honeycomb body has been formed by stacking planar bands and corrugated bands, each of which is made from a heat-resisting steel sheet, in a mutually contiguous relation and rolling them together into a spiral form and defines a number of network-patterned, axial gas flow passages (hereinafter called "cells") for permitting passage of exhaust gas therethrough.

The metallic honeycomb body and the metallic casing are firmly fixed together by brazing or welding them so that the metallic honeycomb body can withstand thermal expansions and thermal stresses - which occur in a high-temperature atmosphere due to the high temperature of the exhaust gas itself and an exothermic reaction of the exhaust gas by the exhaust gas cleaning catalyst - and also extreme vibrations during running of the automotive vehicle.

Needless to say, the planar bands and corrugated bands which make up the metallic honeycomb body are fixed together at at least some of areas of contact therebetween by brazing, welding or mechanical fasten ing to form the metallic honeycomb body into a vibra tion proof structure.

The metallic honeycomb body of the rolled type, a principal element of the above-described metallic car rier body, is superior in various aspects to the ceramic-made monolithic honeycomb body. There is how ever room for a further improvement with respect to large thermal stresses which occur under the severe thermal conditions described above.

In particular, an unduly large thermal stress concentrates on an outer peripheral portion of the metallic honeycomb body, said portion being in contact with an inner peripheral wall of the metallic casing, or a portion adjacent to the outer peripheral portion.

The planar bands and corrugated bands of the metallic honeycomb body are therefore buckled, cracked or other wise damaged so that the durability of the metallic carrier body is reduced.

As replacements for metallic honeycomb bodies of the above-described spirally rolled type, metallic honeycomb bodies having a honeycomb structure have been proposed recently. Each of these replacement metallic honeycomb bodies has the structure that, in each mini mum unit making up the metallic honeycomb body, namely, in each minimum unit composed in combination of a planar band and a corrugated band arranged in a con tiguous relation, the minimum unit is maintained at op- posite end portions thereof in contact with an inner wall of an associated metallic casing. S-shaped or X wrapped, metallic honeycomb bodies are proposed, for example, in Japanese Patent Application Laid-open (Kokai) Nos. SHO 62-273051, HEI 1-218637 and HEI 4 227855.

In a metallic carrier body of the spirally-rolled type described above, each minimum unit is maintained at only one end portion thereof in contact with the in ner wall of an associated metallic casing. In a metal lic carrier body of the last-mentioned conventional type, however, each of a desired plural number of mini mum units is maintained at both opposite end portions thereof in contact with the inner wall of an associated metallic casing. It is therefore possible to absorb or reduce a thermal stress at each end portion, so that improved durability is obtained.

Incidentally, the terms employed above to indi cate the various shapes of the above-described metallic honeycomb bodies may be regarded as common names as will be described next.

Paying attention to one of the minimum units of a metallic honeycomb body, that is, to one multilayer unit consisting of a planar band and a corrugated band, the metallic honeycomb body is called an 'IS-shaped" metallic honeycomb body where the multilayer unit is curved in the form of letter S when the metallic honeycomb body is viewed at a front face thereof. In a metallic honeycomb body fabricated by making a desired number of stacks, typically four stacks - each being formed of such minimum units superposed one over the other in a desired number of layers - abut at one end portions thereof and then rolling the individual stacks about the abutting end portions thereof, the abutment of the four stacks is in an X-shaped (or swastika) pat tern. Metallic honeycomb bodies of this type are therefore called "X-wrapped" metallic honeycomb bodies.

S-shaped or X-rapped metallic honeycomb bodies, which are different from those of the above-described spirally-rolled type, are accompanied by the following drawbacks:

(i) In an S-shaped metallic honeycomb body, each minimum unit consisting of a planar band and a cor rugated band unavoidably includes sites where the bands are folded over 1800. Especially, the waveform of the corrugated band is therefore deformed because of the application of working stresses. It is therefore im possible to fabricate a metallic honeycomb body having uniform cells.

(ii) In an X-wrapped metallic honeycomb body, the state of abutment of each stack at a central part is such that the end portions of the individual planar band and corrugated bands of the stack are arranged in abutment against a planar band forming an outermost layer of the adjacent stack. In other words, the end portions of the individual bands forming each stack are abutted and fixed by brazing or the like at edges thereof in a point-to-point fashion to an outermost planar band of the adjacent stack. The mutual abutment and fixed securement of the individual stacks are not sufficient and, when deforming force due to a thermal stress, vibrations or the like is applied to the abutted portions, the durability of the metallic honeycomb body is significantly deteriorated.

As has been described above, metallic honeycomb bodies other than those of the spirally-rolled type, especially X-wrapped metallic honeycomb bodies there fore require special consideration to the durability of their central parts because of their structures.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an X-wrapped metallic honeycomb body excellent in durability by incorporating durability-improving means in a central part thereof.

In one aspect of the present invention, there is thus provided an X-wrapped metallic honeycomb body for carrying thereon an exhaust gas cleaning catalyst, said body having been constructed using at least two stacks each of which comprises planar band(s) and corrugated band(s) made from metal sheets and alternately stacked into a desired number of layers, characterized in that:

(i) each of the stacks has a notched fitting por tion so that the stacks are mutually fitted together at the notched fitting portions thereof; and (ii) the stacks have been rolled in the same direction about the notched fitting portions thereof as a central axis of the rolling formation.

Preferably, the notched fitting portion of each stack can be formed at a longitudinal central part thereof. The notched fitting portion of each stack may be in such a desired shape that, when the respective stacks are stacked and combined together at the notched fitting portions thereof, the resulting X-wrapped metallic honeycomb body is assured to have a flush front face and a flush rear end face.

The term "notched" as used herein shall not be construed to limit the shape of the notched fitting portion to any particular shape insofar as the above object of the present invention is attained.

8 The X-wrapped metallic honeycomb body according to the present invention is different from any metallic honeycomb body which is fabricated by abutting and fixing stacks at one end portions thereof, for example, four stacks at one end portions thereof into the form of letter X or a cross and then rolling them in the same direction.

The X-wrapped metallic honeycomb body according to the present invention is fabricated by providing as the individual stacks those having mutually-fitting, notched fitting portions, mutually fitting and combin ing the stacks at the notched fitting portions and then rolling in the same direction the thus-combined stacks, for example, two stacks fitted and fixed together in the form of letter X or a cross at the notched fitting portions.

The X-wrapped metallic honeycomb body according to the present invention does not use the fabrication method that, as in the conventional X-wrapped metallic honeycomb bodies, individual stacks are abutted and fixed together at one end portions thereof. The indi vidual stacks are fitted and combined together, so that the X-wrapped metallic honeycomb body according to the present invention has excellent durability, especially at the center of its rolled structure.

In a conventional X-wrapped metallic honeycomb body, its central part is subjected to large thermal stresses and severe vibrations, leading to the poten tial problems that the abutted portions of its individ ual stacks may be separated and the individual bands (planar bands and corrugated bands) may be cracked or otherwise damaged due to the separation. In the X wrapped metallic honeycomb body according to the pres ent invention, however, such potential problems are prevented or reduced and further, falling of carried catalyst layers and a reduction in the cleaning ef ficiency of exhaust gas - which are induced in associa tion with such problems - can be effectively prevented or reduced.

In the X-wrapped metallic honeycomb body accord ing to the present invention, its structural elements, that is, the individual stacks are fitted and fixed to gether at the center of the rolled structure. It is therefore possible to prevent or otherwise reduce tele scoping which tends to occur at a central part of a conventional X-wrapped metallic honeycomb body. The term "telescopingU means the phenomenon that the cen tral part of the metallic honeycomb body is caused to project out in an axial direction due to thermal stresses, and is also called "filming-out". The pre- vention or reduction of telescoping has become feasible because thermal stresses are divided at the fitting portions and deforming forces interfere with each other there.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of individual stacks forming an X-wrapped metallic honeycomb body according to a first embodiment of the present invention; FIG. 2 is a front view of the stacks forming the X-wrapped metallic honeycomb body according to the first embodiment of the present invention, in which the stacks have been fitted and combined together; FIG. 3 is a front view of a metallic carrier body making use of the X-wrapped metallic honeycomb body ac cording to the first embodiment of the present inven tion; FIG. 4 is a front view of stacks forming an X wrapped metallic honeycomb body according to a second embodiment of the present invention, in which the stacks have been fitted and combined together; FIG. 5 is a perspective view of the second stack forming the X-wrapped metallic honeycomb body according to the second embodiment of the present invention; FIG. 6 is a front view of a metallic carrier body making use of the X-wrapped metallic honeycomb body ac cording to the second embodiment of the present inven tion; FIG. 7 is a front view of a metallic carrier body making use of an X-wrapped metallic honeycomb body ac cording to a third embodiment of the present invention; FIG. 8 is a front view of a metallic carrier body making use of a conventional X-wrapped metallic honeycomb body; and FIG. 9 is an enlarged view of a central part of a front face of the conventional X-wrapped metallic honeycomb body.

DETAILED DESCRIPTION OF THE INVENTION

AND PREFERRED EMBODIMENTS The technical features and preferred embodiments of the present invention will hereinafter be described in detail with reference to the drawings.

It is however to be borne in mind that the pres ent invention shall not be limited to the preferred em- bodiments illustrated in the drawings.

First, a conventional X-wrapped metallic carrier body to which the present invention is applicable for its improvement will be described with reference to drawings.

A X-wrapped metallic carrier body MC1 of the above conventional type is illustrated in FIG. 8.

The X-wrapped metallic carrier body MC1 is com posed of an X-rapped metallic honeycomb body XHI and a metallic casing Cl in which the honeycomb body XHI is accommodated and fixed.

The cross-sectional shape of each X-wrapped metallic carrier body according to the present inven tion is not limited to the one shown in FIG. 8 but can include an oval shape, a racetrack shape and the like disclosed, for example, in Japanese Patent Application Laid-Open (Kokai) No. HEI 4-227855.

The metallic honeycomb body XHI which is the principal element of the above-described conventional X-wrapped metallic carrier body MC1 is fabricated by a process which comprises (a) providing at least two stacks individually formed by alternately stacking planar bands and corrugated bands, each made from a metal sheet, one over the other into a desired number of layers, (b) bringing the individual stacks into abutment against each other at abutting end portions thereof, said end portions being located at one ends of the stacks, by using a desired jig or the like and then (c) rolling the thus-abutted composite body in the same direction about the abutting end portions.

The X-wrapped metallic honeycomb body XHI shown in FIG. 8 has been formed by forming four stacks V, to xl 4 in the step (a), bringing the individual stacks into abutment at abutting end portions thereof, said end portions being located at one ends of the stacks, at a crossing angle of 900 in the step (b) and then rolling the resultant composite body about the abutting end portions in the step (c).

In the conventional X-wrapped metallic honeycomb is body XHI described above, the durability of its por tions abutting the metallic casing C' (see FIG. 8) and portions adjacent to the former portions has been im proved for the above-described reasons. The conven tional X-wrapped metallic honeycomb body XHI, however, has the following drawback.

In the central part of the X-wrapped metallic carrier body XHI shown in FIG. 9, attention is drawn to the first stack V, and the fourth stack X4. As is illustrate in FIG. 9, abutting end portions of the first stack X', abut at right angles against a planar band (sheet metal) forming an outermost layer of the fourth stack X14.

When the abutting portions are observed micro scopically, edge portions of the abutting portions of individual planar bands 11 and corrugated bands 21 forming the first stack V, abut as lines at right angles against the planar band of the fourth stack X14 (line abutment). Even if the abutting portions are fixed by brazing or the like, no fully-fixed state can be obtained. When large thermal stresses and/or vibra tions are applied to the fixed portions during the metallic carrier body XHI is used, the abutting por tions may be separated and, due to the separation, the bands 11,21 may be cracked or otherwise damaged. The durability is therefore impaired substantially. in FIG. 9, numeral 31 indicates cells.

The individual stacks X11 to XIn which make up the X-wrapped metallic honeycomb body XHI are not limited to the above-described ones shown in FIGS. 8 and 9, and stacks of various shapes and structures can be adopted. The above description applies equally to such stacks.

As described above, the present invention has a greatest characteristic feature in that means for im proving the durability of a central part has been in- corporated in view of the low durability at the central part of the conventional X-wrapped metallic hcneycomb body XHI.

Therefore, the present invention features that it does not adopt the method that, as in the conventional structure, a desired number of stacks V, to X'n, n being an integer of at least 2, forming an X-wrapped metallic honeycomb body XHI are simply abutted against each other at abutting end portions located at one ends of the individual ends.

The present invention has a characteristic fea ture in that - as individual stacks X1 to Xn, n being an integer of at least 2, making up an X-wrapped metal lic honeycomb body M - those provided at central parts thereof with mutually-fitting, notched fitting portions A are adopted.

In particular, preferred as the structure of the notched portions of the notched fitting portions A of the individual stacks X, to Xn is such a structure that (1) the individual stacks X1 to Xn can be fitted to gether at the central parts thereof and (2) when the individual stacks X, to Xn are fitted together at the notched fitting portions thereof and then rolled in the same direction about the notched fitting portions as a central axis of the rolling formation into the X- wrapped metallic honeycomb body XH, the X-wrapped metallic honeycomb body is assured to form a front end face XHf and a rear end face XHb, preferably a flush front end face XHf and a flush rear end face XHb lying in common planes, respectively.

With reference to the drawings, a description will hereinafter be made of means for improving the durability of the central part of the X-wrapped metal lic honeycomb body M according to the present inven tion, more specifically of the notched fitting portions provided at the central parts of the individual stacks X1 to Xn.

Referring to FIGS. 1 to 3, the X-wrapped honeycomb body M according to the first embodiment of is the present invention will now be described. The X wrapped honeycomi> body XH has been improved in durability at a central part thereof and is useful for the fabrication of an X-wrapped metallic carrier body.

As is shown in these drawings, the individual stacks X1 to X2 have been formed by alternately stack ing planar bands 1 and corrugated bands 2 one over the other into a predetermined number of layers and provid ing notched fitting portions A, to A2 at central parts of the individual stacks. The planar bands 1 are each made of a sheet metal, while the corrugated bands have been obtained by corrugating such planar bands.

The notched fitting portions A1 to A2 ptuvided at the central parts of the individual stacks X, to X2 preferably have such a shape that, when the individual stacks are fitted and combined together (the state shown in FIG. 2) and are then rolled in the same direc tion about the notched fitting portions as a central axis of the rolling formation into the X-wrapped metal lic honeycomb body XH (the state depicted in FIG. 3), the front face XHf and rear face XHb of the metallic honeycomb body XH are flush in common planes, respec tively.

As the planar bands 1 employed to fabricate the X-wrapped metallic honeycomb body in the present inven tion, it is possible to use bands employed for the fabrication of conventional main converters (Me) of the monolithic metal type, for example, bands having a thickness of from 0.04 mm to 0.1 mm and made, for exam ple, of a chromium steel (chromium content: 13-25%), a heat-resistant stainless steel such as Fe-20% Cr-5% Al, or a heat-resistant stainless steel formed by adding a rare earth metal to the first-mentioned stainless steel to improve the high-temperature oxidation resistance.

Further, usable examples of the corrugated bands 2 in clude those obtained by corrugating such planar bands to have a predetermined, substantially sinusoidal or trapezoidal waveform.

Particularly preferred as the planar bands 1 and corrugated bands 2 are those obtained by subjecting planar and corrugated bands, which contain Al or carry an Al layer on surfaces thereof, to heat treatment so that a layer of alumina (A1203) in the form of whiskers or mushrooms is deposited on the surfaces thereof.

Layers of whisker-shaped alumina are preferred because they can firmly hold thereon a wash coat layer for carrying thereon an exhaust gas cleaning catalysts such as Pt, Pd and Rh.

In the present invention, the metallic carrier body MC shown in FIG. 3 is fabricated as described above, namely, by fitting and combining individual stacks X1 to Xn together at notched fitting portions thereof, rolling them about the notched fitting por tions into a metallic honeycomb body M and then fixing the metallic honeycomb body M in a metallic casing C.

The metallic casing C is employed to accommodate and fix the X-wrapped metallic honeycomb body XH there in. No particular limitation is imposed on the metal lic casing C insofar as it is open at opposite ends thereof and has the same cross-sectional shape as the metallic honeycomb body M.

As the material of the metallic casing C, it is possible to use a heat-resistant steel of the _zame type as that of the bands 1,2 forming the honeycomb body or to use a material having still higher heat and corro sion resistance. It is also possible to use a material of such a double-layer structure that a metal material of an outer layer has higher heat and corrosion resistance than that of an inner layer, and specifical ly a double-layer material in which ferritic stainless steel is used for an inner layer and austenitic stain less steel is used for an outer layer.

Referring next to FIGS. 4 to 6, a description will next be made of the X-wrapped metallic honeycomb body M according to the second embodiment of the pres is ent invention. THe X-wrapped metallic honeycomb body M possesses improved durability at a central part thereof.

As shown in FIG. 4, three stacks X, to X3 are used in the second embodiment.

FIG. 4 corresponds to FIG. 2 of the first embodi ment described above.

In the second embodiment of the present inven tion, the stack shown X2 shown in FIG. 5 can be used as a second (middle) stack. No particular limitation is imposed on the shape or structure of each notched fit- ting portion A provided at a central part of the second (middle) stack X2 as long as it can be fitted with a first stack X, and a third stack X3 in such an arrange ment as illustrated in FIG. 4. Namely, the notched fitting portions of the first to third stacks X1 to X3 are only required to have such shapes that the first stack X, and the third stack X3 can be fitted in the second stack X2 from front and rear sides thereof, respectively, with the first stack X, and the third stack X3 forming a crossing angle of 1200 therebetween (i.e., a crossing angle of 600 relative to the second stack X2).

The third embodiment of the present invention will next be described with reference to FIG. 1. The third embodiment is therefore not illustrated in any of the drawings. Stacks are provided with notched fitting portions in the following relationship:

H > h, + h2 wherein hl,h2: Depths of the notched fitting portions Al,A2 of the individual stacks X1,X2, and H: Height of the respective stacks XliX2 (Incidentally, the height governs the width of a metallic honeycomb body when 25 the stacks are formed into a metallic honeycomb body.).

In such an embodiment as the third embodiment, a space is formed at the notched fitting portions when the respective stacks are fitted together. When an X wrapped metallic honeycomb body (M) is fabricated from such a composite body, a space of a desired volume is formed at an axial central part and deforming forces developed by thermal stresses can be effectively ab sorbed and reduced in the space.

The fourth embodiment of the present invention will next be described with reference to FIG. 7. The shape of each X-wrapped metallic honeycomb body M ac cording to the present invention is not limited to such a circular cross-section as in the first embodiment is but, as shown in FIG. 7, may be in the form of a racetrack as viewed in a cross-section.

22

Claims

CLAIMS:

1 1. An X-wrapped metallic honeycomb body for car 2 rying thereon an exhaust gas cleaning catalyst, said 3 body having been constructed using at least two stacks 4 each of which comprises planar band(s) and corrugated band(s) made from metal sheets and alternately stacked 6 into a desired number of layers, characterized in that:

7 (i) each of the stacks has a notched fitting por 8 tion so that the stacks are mutually fitted together at 9 the notched fitting portions thereof; and (ii) the stacks have been rolled in the same 11 direction about the notched fitting portions thereof as 12 a central axis of the rolling formation.

1
2. An X-wrapped metallic honeycomb body accord 2 ing to claim 1, wherein the notched fitting portion of 3 each stack is formed at a longitudinal central part 4 thereof.

1
3. An X-wrapped metallic honeycomb body accord 2 ing to claim 2, wherein the notched fitting portion of 3 each stack is in such a shape that, when the respective 4 stacks are stacked and combined together at the notched fitting portions thereof, the resulting X-wrapped 6 metallic honeycomb body is assured to have a flush 7 front face and a flush rear end face.

1
4. An X-wrapped metallic honeycomb body accord- 2 ing to any one of claims 1 to 3, wherein the honeycomb 3 body is constructed of two stacks.

1
5. An X-wrapped metallic honeycomb body accord- 2 ing to any one of claims 1 to 3, wherein the honeycomb 3 body is constructed of three stacks.

1
6. An X-wrapped metallic honeycomb body as 2 hereinbefore described with reference to, and as shown 3 in, the accomanying drawings.